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Techniques and Methods 10–C10

Determination of the (³⁴S/³²S) of Sulfate in Water: RSIL Lab Code 1951

U.S. Geological Survey

By Kinga Révész and Haiping Qi

This report is available as a pdf.

Summary of Procedure

The purpose of Reston Stable Isotope Laboratory Lab (RSIL) Code 1951 is to determine the δ³⁴S isotopic composition of dissolved sulfate. Dissolved sulfate is collected in the field and precipitated with BaCl₂ at pH 3–4 as BaSO₄ in the laboratory. However, the dissolved organic sulfur (DOS) is oxidized to SO₂, and the carbonate is acidified to CO₂. Both are degassed from the water sample before the sulfate is precipitated. The precipitated BaSO₄ is filtered and dried before introduction into an elemental analyzer (EA)(Carlo Erba NA 2500). The EA is used to convert S in a BaSO₄ solid sample into SO₂ gas, and the EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the sulfur isotopes ratio of the product SO₂ gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in a tin capsule and loaded into the Costech Zero-Blank Autosampler of the EA. Under computer control, samples are dropped into a heated tube reaction tube that combines the oxidation and reduction reactions. The combustion takes place in a He atmosphere containing an excess of oxygen gas at the oxidation zone at the top of the reaction tube. Combustion products are transported by a He carrier through the reduction zone at the bottom of the reaction tube to remove excess oxygen and through a separate drying tube to remove any water. The gas-phase products, mainly CO₂, N₂, and SO₂, are separated by a gas chromatograph (GC). The gas is then introduced into the isotope-ratio mass spectrometer (IRMS) through a Finnigan ConFlo II interface, which also is used to inject SO₂ reference gas and He for sample dilution. The IRMS is a Thermo-Finnigan Delta^Plus CF-IRMS. It has a universal triple collector with two wide cups and a narrow cup in the middle. It is capable of measuring mass/charge (m/z) 64 and 66 simultaneously. The ion beams from SO₂ are as follows: m/z 64 = SO₂ = ³²S¹⁶O¹⁶O; 66 = SO₂ = ³⁴S¹⁶O¹⁶O primarily.

Table of Contents

Preface

Conversion Factors, Acronyms, and Abbreviations

Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentation

Reference Materials Used, Storage Requirements, and Shelf Life

Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Holding Times, and Disposal

Sample Containers, Preservation, and Handling Requirements

Sample Preparation and Time Requirements

Performing the Analysis and Time Requirements

Problematic Samples

Interferences

Troubleshooting and Bench Notes

Maintenance and Maintenance Records

Sample Retention Time and Disposal

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance

Laboratory Information Management System for Light Stable Isotope (LIMS-LSI)

Quality-Control (QC) Samples

Acceptance Criteria for all QC Samples

Corrective Action Requirements

Responsible Parties for All QA/QC Functions for Procedures Covered in RSIL SOPs

Data Management and Records

Health, Safety, and Waste-Disposal Information

Applicable Health and (or) Safety Issues

Personal Protection

Electrical Hazards

Chemical Hazards

Gas Cylinder Handling

Specific Waste-Disposal Requirements

Revision History

References Cited

Apendixes

A.	Step-by-Step Procedure to Log-in Samples to LIMS-LSI
B.	Step-by-Step Procedure to Precipitate BaSO4
C.	Step-by-Step Procedure to Generate an Excel Sample Workbook or to Print a Template and a Sample to Be Analyzed List
D.	Step-by-Step Procedure for Weighing and Storing Samples
E.	Step-by-Step Procedure for Zero Blank Auto Sampler Operation
F.	Step-by-Step Procedure to Add Sample Information to Sequence Table
G.	Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 for LIMS-LSI and for Data Back-Up
H.	Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to Back-Up Computer, and to Reevaluate Old Data
I.	Step-by-Step Procedure to Determine and Apply Correction Factors and Evaluate Data
J.	Step-by-Step Procedure to Check Elemental Analyzer for Leaks
K.	Daily Check List
L.	Changing the Insertion Tube
M.	Changing the Water-Trap
N.	Changing the Reaction Tube
O.	Step-by-Step Procedure to Report Data

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